Patent GB-367251-A (GB)
Title: Improvements in altimeters and rate of climb indicators
IPC: G01L7/00
Filed: 1931-05-08
Abstract: 367,251. Altimeters and rate of climb indicators. PIONEER INSTRUMENT CO., Inc., 754, Lexington Avenue, Brooklyn, New York, U.S.A. May 8, 1931, No. 13678. Convention date, May 10, 1930. [Class 106 (ii).] Comprises an altimeter or rate of climb indicator characterized by the fact that it is provided with means for automatically putting the interior of the expansible chamber in communication with the atmosphere to prevent the pressure acting upon the expansible chamber or the displacement of this chamber exceeding a predetermined limit. The Figure shows a form which is convertible from a rate of climb instrument to an altimeter. The closed casing 10 forms a chamber 13 always open to the atmosphere through a fitting 14 and perforated pipe 17. Most of the internal fittings are attached to the wall 12 and may be tested before assembly. The wall 12 carries a post20 to a boss 21 on which is attached a spring member 22 which may be adjusted by a screw 23. The member 22 carries a diaphragm chamber 24. The post 20 also has an extending arm 26 to which a lever 27 is pivoted at the point 28. The arm 29 of this lever is pivoted to a link 30 pivoted at the point 31 to the movable end of the diaphragm chamber 24. The free end 32 of the other arm of the lever 27 is connected by a flexible member 33 to a drum 34 about which it is wound. The drum 34 and pointer 35 rotate about the spindle 36 according to the movements of the chamber 24. A hair spring 37 takes up any slack in the member 33. A heat insulated tank 41 is connected by a conduit 42 through the chamber 43 and a conduit 44 with the expansible chamber 24. The post 20 carries an arm 47 to which is fastened one end of a resilient member 48 the free end of which rests on a plate 49 mounted on a pivot 50. The member 48 carries a valve 51 which normally closes the end of a tube 53 which communicates with the chamber 43. The link 30 carries a pair of fingers 54, 55 which contact with the plate 49 when the chamber 24 has reached the limits of its permissible movement in either direction. Whenever contact is established, the plate 49 will be tilted to move the member 48 and open the valve 51 thus placing the interior of the chamber 24 in communication with the atmosphere. When used on aircraft, the opening would occur when the aircraft has descended below a certain elevation and when it has risen above a certain elevation. The pressure of the air within the chamber 24 may be made to correspond with the atmospheric pressure at any desired elevation to form a datum or reference elevation by means of a valve which may be opened sufficiently long to permit equalization of the pressure within and without the chamber at the given elevation and thereafter closed. This valve may be fitted instead of the member 58 which is not necessary when the instrument is solely an altimeter. The member 58 carries a capillary tube 59 surrounded by a cap 62 and a restricted passage is thus formed between the chamber 43 and the atmosphere via the tube 59, passage 60 between tube and cap, tube 63 and a tube 64 connected to the fitting 14. A needle valve 65 operated by a handle 68 is fitted for adjusting the degree of opening at the junction of pipes 63, 64. In a modification, the valve 51 is carried on a spring strip and is opened automatically when the pressure inside the chamber exceeds a predetermined amount.